Calliphoridae, blow flies, bluebottles, greenbottles.

These are commonly known as bluebottles, greenbottles and blowflies. There are 38 British species. The adults range in length from 5 - 15 mm. The larvae feed on carrion and decaying matter. The adult mouthparts are similar to those of Musca domestica below. Many of the adults are a metallic green or blue, and have bristles all over their body.

Because most of the larvae feed on vertebrate carrion, species in this family have become very important in forensic entomology as the rates of developments of the larvae of different species can indicate the time of death. Blowfly larvae are also used in medicine in "maggot therapy" where they are used to clean up wounds. The greenbottle Lucilia sericata is the most commonly used species. Anglers also use blowfly larvae as bait.

The genus Calliphora contains the bluebottles, and the genus Lucilia contains the greenbottles.

Above right
is a preserved specimen of the common bluebottle, Calliphora vomitoria, and on the left a close-up of the head. It breeds throughout the year. Adults have a bluish metallic abdomen. Note the huge eyes, the two sausage-shaped things are part of the aristate antennae, adult length is 10 -12 mm. It is usually the females that we find in our houses, as they search for meat or fish on which to lay their eggs. The males tend to stay outside basking and drinking nectar from flowers.

The female lays her eggs on carcasses, open wounds or rotting meat for her larva to feed on. The eggs are creamy white, and 1.5 mm long, and can hatch within a day. A female can lay up to 600 eggs in her life time. The pupa is a dull red/brown.

Taste discrimination in blowflies

Adult flies taste with their feet, and on the last tarsal segment they have gustatory bristles and taste hairs. These hairs have a pore at the end into which a stimulus can enter to reach the sensory cells.

There are five sensory cells in each hair; one mechanoreceptor which detects bending, two which respond to salts (one to anions the other to cations), one responds to sugar, and one to water.

The feet perform preliminary tasting of substances. If these substances are acceptable as food or water then the fly will extend its proboscis. This preliminary tasting prevents the fly from tasting harmful substances with its proboscis as the fly doesn't actually take in any food until it has passed the chemical tasting of its tarsal hairs and also the hairs around the edge of the labellum, which work in the same way as the tarsal taste hairs.

On the right is the pupa of a blowfly. The bars on the ruler are at 1 mm intervals. The pupa has a hard skin. When the adult fly is ready to emerge from the pupa the fly inflates a small bladder on the top if its head. This bladder presses against a weak point in the top of the pupa causing a circular rupture in its wall which pops upwards to form a lid allowing the adult flu to escape.

Muscidae, house flies

Found worldwide. There are over 3000 species, and 282 British species. Most feed on liquids by lapping them up with their spongy mouthparts (see right), but there are a few blood-suckers and predators in the family. The larvae feed mainly on dung and decaying matter. Many are pests of livestock and vectors of disease. Most British adults are grey or black.

Musca domestica, the common house fly

The female deposits her white, cigar-shaped eggs in manure or rotting refuse. The cigar-shaped egg is around 1 mm long and glistening white. They are laid in batches of 12 - 150, and a female can lay up to 900 eggs in her lifetime. She will lay every 10 days or so. In theory one pair of adults could give rise to 190 million billion flies in 3 - 4 months!

Above are the lapping mouthparts of a house fly.

Within 24 hours the white legless larva or maggot (see left) hatches and starts to eat its surroundings. Before another 24 hours have passed it has grown so much in size that it must moult its skin. Under normal circumstances it eats so much and so quickly that it moults 3 times in 3 days. A fully grown larva is 10 - 12 mm long. The head end is small and pointed. Then on the fourth day it crawls away and burrows underground where it pupates for about 3 days. It can burrow up up to 30 cm deep to pupate. In the drawing on the left it is the pointed end that is the head. It can withdraw its head into its body for protection.

The pupa is barrel-shaped, pale yellow at first, but darkens to brown/black. So from egg to adult takes around a week to 10 days. The adult fly emerges from the more pointed end of the pupal case.

The adult fly (see right) emerges, tunnels upwards to the surface to begin its adult life which lasts around 2 months. The body length is from 3 - 12 mm. It has a grey body with 4 black lines down its thorax. Within a week of hatching into an adult the female, once mated, is ready to lay her first batch of around 100 eggs. The adult feeds off rotting garbage as well as fresh food, and because of its pads of sticky hairs on its feet (see the drawing on the right) it picks up and spreads germs. It is a carrier of typhoid, dysentery, diarrhoea, and in warmer regions cholera, yaws and opthalmia.

Foot. The leg ends in 2 claws (see right), each with a hair-covered pad underneath. When the pad is pressed the hairs exude a sticky fluid, so enabling the fly to walk on most surfaces.

The biggest predators of house flies, apart from man, are spiders, toads, lizards and birds. Flight speed has been recorded as 2.0 metres per second with a wing beat of 190 per second. Compare this with other insects.

Housefly Head and mouthparts

Its mouthparts are soft and end in spongy pads, see above right and left, and it feeds only on liquids. So how does it feed off a sugar lump or other solids? Well it regurgitates part of its last meal on to its next meal. This liquid and the enzymes in it soften and liquefy part of the solid which the fly then mops up. This is another way of spreading germs. Also it frequently defecates while feeding.

It has been found that 5 million bacteria can be found on the body surface of a single adult! It has also been found that an individual will fly as far as 20 miles to reach a good source of food. So the fly that landed briefly on your sugar bowl or, even worse, on the rim of your glass, can easily have flown from any source of sewage or manure within a 20 mile radius.

Like most adult insects it has 2 compound and 3 simple (ocelli) eyes.

Overwintering. Most adult houseflies will die with the onset of cold weather, however some can survive the winter, and some will overwinter as pupa.

Deception. On an island off the Sardinian coast the dead horse plant, an arum lily, Helicodiceros sp. gives off a perfume of rotting meat. This attracts blow flies who normally lay their eggs on rotting meat on which the larvae need to feed when they hatch. The flies land on the plant and make their way to the source of the smell inside the flower. The structure inside is very elaborate, and on the way down there are guard hairs prohibiting escape. The flies are trapped inside the flower. The flies can feed on nectar and lay their eggs, however the larvae will die as there is nothing for them to feed on when they hatch. On the second day the stamens shower the captive blow flies with sticky pollen. And on the third day the guard hairs wither and the flies can escape to pollinate other Helicodiceros as the pollen rubs off their bodies as they make their way down inside another flower.

Mesembrina meridiana

On the left and below is Mesembrina meridiana one of the largest British Muscids. The adult reaches 10 - 12 mm long. It is often found sunbathing on walls and flowers from early spring until late autumn. It is especially fond of umbelliferous flowers where it drinks nectar.

The female lays her eggs singly in horse or cow dung. The egg is 4.5 mm long, and hatches almost immediately.

Below left is a close up of the yellow patches on the face, and below the claws and pads of the foot.